Method of making pellucid laminates having an interference filter



Aug. 11, 1970 J. w. EDWARDS METHOD OF MAKING PELLUCID LAMINATES HAVING AN INTERFERENCE FILTER Original Filed Jan. 4, 1965 lll/1111 l /r 111// I 5 1 l j 1 l, 1 l I f FIG. I \l FIG. 2

Flc-,.3 l 'l FIG. 4

4 Sheets-Sheet 1 Ca I/ FIG.6

INVENTOR JAMES W. EDWARDS @MMM ATTORNEY Aug. l1., 1970 J. w. EDWARDS 3,523,847

METHOD OF MAKING PELLUCID LAMINATES HAVING AN INTERFERENCE FILTER Original Filed Jan- 4, 1965 4 Sheets-Sheet 2 RAY DIAGRAM FOR COATED GLASS FIG. 8 FOR INCIDENCE oN GLASS SIDE GLAss PLASTIC LAYER coATING INCIDENT PANEL ENERGY TLN-02 (1- 9 la 3(1` l y@ *Q03 j vg! r 6J, a /\Jh CQ c o )r 5 Y ABSORBED INVENTOR JAMES W. EDWARDS ATTORNEY Aug. l1, 1970 J. w. EDWARDS 3,523,847

l METHOD OF MAKING PELLUCID LAMINATES HAVING I AN INTERFERENCE FILTER' Original Filed Jan. 4, 1965 4 SheetsfSheet :s

F|G 9 RAY DIAGRAM FOR COATED GLASS FOR INCIDENCE ON COATED SIDE COATING PLASTiC LAYER GLASS PANEL INCIDENT ENERGY Pl N rl=rc a1c=ac tx=t 1(1-0) 2 (g1r o TRANSMITTED J t T2 r REFLETED azcc pac 3 tftcr nrc(1o) *t 13b a=t1pra Sgc s a 2 a A 4 v INVENTOR JAMES W. EDWARDS www ATTORNEY Aug- 11, 1970 VJ. w.-EDwARDs 3,523,847

. METHOD oF MAKING PELLUCID LAMINATES HAVING AN INTERFERENCE FILTER Original Filed Jan. 4, 1965 4 Sheets-Sheet 4 ATTORNEY Unted States Patent O 3,523,847 METHOD OF MAKING PELLUCID LAMINATES HAVING AN INTERFERENCE FILTER James W. Edwards, St. Louis, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Original application Jan. 4, 1965, Ser. No. 423,263. Divided and this application Aug. 1, 1969, Ser. No. 846,761

Int. Cl. C03c 27/04 U.S. Cl. 156-99 8 Claims ABSTRACT OF THE DISCLOSURE A method of making a pellucid laminate having a pair of outer panels with at least one interference filter disposed between the outer and inner panels. The method includes the locating of a relatively thin plastic member, a multilayer dielectric lm serving as an interference filter, a monolayer film and a plastic support member in marginal registration and laminating these components to form an optical device.

This application is a division of my copending application Ser. No. 423,263 filed Jan. 4, 1965.

This invention relates in general to certain new and useful improvements in thin film optics, and more particularly to laminated structures employing optically thin films in combination with absorbing media which are suitable for altering the optical characteristics of transparent medias.

In the past few years, there has been an increasing tendency to construct buildings with non-load bearing walls or so-called curtain wall buildings and which employ glass extensively as the wall structure. However, large window areas create a number of serious problems, the foremost of which are glare and heat gain from direct solar radiation. It has been estimated that the extra load on air conditioning equipment caused by heat absorbed in the visible light from the sun increases the initial cost of air conditioning equipment from 33 to 50%. Initial installation costs of air conditioning to remove heat admitted as solar radiation frequently averages about ten cents per B.t.u. per hour per square foot. Peak solar radiation admitted by regular glass ranges between approximately 100 and 200 B.t.u. per hour per square foot. Therefore, the added cost for air conditioning per square foot of regular unshaded window glass due to solar radiation over a three to four hour period has been averaged to be approximately ten dollars ($10.00) to twenty dollars ($20.00) per square foot of window area. In order to obviate this problem, the windows are usually covered with blinds, shades, awnings and similar devices such as vertical louvers to reduce heat radiation with the result that the windows no longer serve their primary function as a viewing panel.

Another problem caused by solar radiation is that of glare or the amount of harshness in transmitted light. In the past, the elimination or reduction of glare has been accomplished by shading devices of the type above described. Glare has also been reduced in the past by architectural design such as large overhangs and deep window reveals. However, all of these methods of reducing glare and heat add to the initial cost and subsequent maintenance of the building and more importantly, reduce the effectiveness of the window for its primary purpose.

There have been many approaches to the designing of window glass in order to solve many of these fenestration problems. In the past, most of the efforts have been directed to the incorporation of various color reducing and glare reducing compounds to the liquid glass composition during the manufacture of sheet glass. Accordingly, there are many commercially available heat absorbing glasses, light absorbing glasses and combination heat and light absorbing glasses. By heat absorption alone, up to 50 percent of the normally transmitted solar radiation can be halted. However, the absorbing of heat by the glass causes considerable rise in the temperature of the glass so that a large portion of the energy which has been absorbed is actually reradiated to the interior of the structure. Thus, heat absorbing glass is not considered to be very efficient in order to solve these fenestration problems. This type of heat absorbing glass also admits excessive amounts of glare. In order to reduce the glare, it is necessary to resort to shading devices of the aforementioned type, which in effect, renders the heat absorbing properties of the glass useless.

Glare reducing glasses which function by absorption of visible light contribute significantly to eye comfort to exposures illuminated by direct solar radiation when their visible transmittance is within the range of 10 to 20 percent. However, conventional types of glare reducing glass transmit a great deal of radiation within infrared radiation wave lengths and hence are not capableof reflecting the heat bearing radiation. The visible light absorption also causes a heating of the glass panel and a condition of re-radiation as infrared energy to the interior of the structure. This re-radiation of long wave length infrared radiation contributes significantly to the heat load in any particular structure.

In an attempt to obviate many of these fenestration problems, various filters have been deposited on the glass surfaces in order to reduce absorption of the heat bearing infrared radiation contained within solar radiation and to reduce glare. A very effective Way of reducing the solar heat load is through the use of partially transparent metal films such as the type described in U.S. Pat. No. 3,069,301. The structures described in this patent provide up to 70 percent total solar heat rejection of which a large part, approximately 52.3 percent of the incident energy, is directly reflected. Moreover, eye comfort is maintained inasmuch as visible transmittance is only 13 percent of the total solar energy maintained upon the glass. While this type of window panel is very effective in reducing the transmittance of infrared radiation, it has limited use because of its high visible reflectance. The high visible reflectance of the glass produces a mirror-like effect and this may be useful as a highlight effect in archis tectural design. However in most architectural applications, it is not desired to have glass with prominence or brilliance which will dominate the structure, but glass panels which will blend inwith the architectural design. Moreover, interference filters of the type described in Pat. No. 3,069,301 often create undesirable color effects in the absorbed visible light.

Another approach which has been employed is the use of metallic filters alone or in combination with one or more dielectric layers. However, metallic filters cause mirrorlike effects which are totally undesirable from an architectural point of view. In order to solve the problems encountered with metallic films, there have been recent attempts to employ multilayer interference films with high and low index of refractions, respectively. These reflectors are given certain characteristics whereby they transmit substantial portions of light of one color and reflect substantial portions of light of another color. For example, they may be prepared with reflectance bands above in the infrared wave length range while reflecting about 10% of visible light. Augmented by meda for absorbing significant quantities of visible light to reduce glare, these films can be used in structures to give performance analogous to the metallic films. However, re-

fiectors of this type are extremely sensitive to the angle of incidence of the light that the beam makes with the interference film. Accordingly, light directed at varying angles of incidence provides varying color presentations which are not desirable.

Aside from the optical problems of the interference filters themselves, the production of such filters has presented many difiicult manufacturing problems to overcome. Normally, the filters are disposed upon a rigid but transparent substrate, such as glass or a heavy sheet of plastic. The films are commonly deposited by a conventional chemical deposition method or vaporizing method. These films are suitable for use even when they are not covered or combined in a laminated structure. However, an uncovered film was always subjected to Weather or abrasion and such films are normally destroyed through use. Accordingly, these interference filters have usually been applied to a transparent substrate which is ultimately employed in -a laminated structure. However, during the lamination process, the filter, which may consist of a multilayer film is often distorted. Moreover, the interference filter which may consist of multilayers of metals and metal oxides or other dielectrics often crack and are destroyed to an extent Where the optics of the device are rendered totally unusable.

It is therefore the primary object of the present linvention to provide a pellucid laminate with an optically thin dichroic filter which can be manufactured without materially altering the optical characteristics of the dichroic filter.

It is another object of the present invention to provide a pellucid laminate containing an optically thin dichroic filter of the type stated which, having a suitable light absorbing medium, is capable of reflecting substantially all of the heat-bearing infrared light contained in solar radiation while transmitting a controlled portion of the visible light.

It is a further object of the present invention to provide transparent laminates with optically thin films of the type stated which are capable of selectively altering the color of the transmitted visible light without materially affecting the quality or color fidelity of transmitted visible radiation. It is an additional object of the present invention to provide pellucid laminates of the type stated which have high optical clarity and low scattering coefiicients.

It is still another object of the present invention to provide pellucid laminates of the type stated which have high Weather and abrasion resistance and can be mass produced on a minimum cost basis.

It is also an object of the present invention to provide a method of manufacturing optical laminates containing dichroic filters without destroying the filter in the lamination process.

It is another salient object of the present invention to provide pellucid laminates of the type stated which have characteristics of high infrared reflectance, controlled visible light refiectance and transmittance, and a good visual appearance compatible for architectural use.

With the above and other objects in View, my invention resides in the novel features of form, construction, arrangement, and combination of parts presently described and pointed out in the claims.

In the accompany drawings (4 sheets):

FIG. 1 is a schematic front elevational view of a pellucid laminate constructed in accordance with and ernbodying the present invention;

l FIG. 2 is a schematic front elevational view of the separated components forming part of the pellucid laminate prior to the lamination process;

FIG. 3 is an enlarged sectional view showing the details of the component designated as C2 in FIG. 2;

FIG. 4 is an enlarged front elevational view of a modifiedpform of the component designated as C2 in FIG. 2;

FIG. 5 is a schematic front elevational view of the components forming part of the pellucid laminate of FIG.v 1 illustrating a modified form of laminating process;

FIG. 6 is a schematic front elevational View of the components forming part of the pellucid laminate of FIG. 1 illustrating another modified form of laminating process;

FIG. 7 is a schematic front elevational View of the components forming part of the pellucid laminate of FIG. 1 illustrating an additional modified form of laminating process;

FIG. 8 is a schematic view showing the energy distribution in a transparent panel having an optical filter and where radiation is incident upon the side opposite the optical filter;

FIG. 9 is -a schematic view showing the energy distribution in a transparent panel having an optical filter and where radiation is incident upon the side having the optical filter; and

FIG. l0 is a schematic view showing the energy distribution in a combination of the transparent panels of FIGS. 8 and 9 to form a pellucid laminate of the type constructed in accordance with and embodying the present invention.

GENERAL DESCRIPTION Generally speaking, the present invention provides a laminate which includes optical interference and absorption filtering means and a method of producing the laminate. The laminates of the present invention are preferably of a rigid construction and are attained by using panels which are resistant to scratching and to similar types of abrasions. One of the pellucid or transparent panels has a very thin layer of a polymeric plastic on one surface with a thickness in the range of approximately one micron. This plastic coated panel constitutes the rst component of the laminate. This 4panel has a high infrared transmittance and low infrared absorbance so as to readily permit entry of solar infrared to the underlying refiecting films and to permit reflectance of selected wave lengths of radiation. A dichroic filter or so-called interference filter is applied to one surface of a relatively thin plastic sheet which is designed to resist high temperature distortion. Applied to the other side of the latter named plastic sheet is another dichroic filter in the form of a single layer dielectric film. This latter combination forms the second member of the laminate. The third member of the laminate consists of a relatively thick sheet of plastic material such as polyvinyl butyral. This plastic sheet of material is capable of being plasticized and may be incorporated with light absorbent materialsl or the normal color pigments normally found in the area of thin film optics. A fourth member of the laminate comprises the second outer pellucid or transparent panel. Naturally, the panels are transparent in the wave length range of radiation to be transmitted. The lower panel may have some radiation absorbing properties, but it should have a low radiation scattering coefficient to provide optical clarity. The entire structure of the four last` named components are stacked in marginal registration' and placed in a chamber under a vacuum. The components are then heated to a suitable lamination temperature and subjected to pressure to produce a single laminated structure.

As a modification of the present invention, the secondl component comprising the thin plastic sheet wih dichroic filters on opposite sides thereof may be laminated or otherwise adhesively secured to the third component consisting of the relatively thick plastic layer, prior to the final, lamination process. In this latter embodiment, the three components are then stacked in marginal registration and polymerizable plastic is deposited on the upper surface of the dichroic filters. Accordingly, four components are provided which are then stacked in marginal registration and laminated in the manner previously described.

As an additional modification of the present invention, the second component comprising the thin plastic sheet with dichroic filters on opposite sides thereof may be laminated or otherwise adhesively secured to the third component consisting of the relatively thick plastic layer prior to the final lamination process. The thin layer of polymerizable plastic which was previously deposited on the undersurface of one of the transparent panels is thus deposited on the upper surface of the dichroic filter which is supported by the thin plastic sheet. In this embodiment, the three components are then stacked in marginal registration and laminated in the manner previously described.

DETAILED DESCRIPTION Referring now in more detail and by reference characters to the drawings, which illustrate practical embodiments of the present invention, A designates a transparent laminate preferably of rigid construction and attained by using rigid panels 1, 2 which are resistant to scratching and similar abrasive action. Moreover, the panels 1, 2 are non-hydroscopic in nature and can be tinted, transparent or translucent in their nature. Illustrative of the materials from which the panels 1, 2 can be constructed are glass, rigid synthetic plastic materials, both thermoplastic and thermosetting in nature, such as polymethyl methacrylate, polystyrene, polyvinyl chloride, polypropylene, polyethylene terephthalate, cellulose acetate, cellulose nitrate and the like. It is understood that the panels 1, 2 must be transparent in the wave length range of radiation to be transmitted.

Deposited on the underside of the panel 2 is a relatively thin film of plastic material 3 which may be thermoplastic or thermosetting in nature such as polyvinyl butyral, ethylenevinyl acetate, hydrolyzed ethylene-vinyl acetate, silicone polymers, cellulose acetate. and many natural polymers such as rubber latices which have suflicient optical clarity. The most recommended of the aforementioned list of plastics is plasticized polyvinyl butyral. The plastic layer should not be less than 0.5 micron thick and should not be greater than 10.0 microns thick. The glass panel 2 with the plastic layer 3 thus constitutes the first component C1 which is to be used in the laminate A.

A thin plastic supporting layer or sheet 4 having an overall thickness preferably within the range of 0.0025 to 0.0050" is provided with a multilayer dielectric film 5 on one surface thereof. The lower size limitation of the layer 4 is determined so that the layer has sufficient supporting strength. The plastic supporting layer 4 is preferably formed of a regenerated cellulose sheet (cellophane), polyethylene terephthalate (Mylar), polyvinyl butyral, or polyvinyl formal, or any similar type of plastic. The film 5 is located in facewise engagement with the plastic layer 3 substantially as shown in FIG. 1. Construction of the multilayer optical film S is more fully described in my copending application Ser. No. 299,851, filed Aug. 5, 1963, and consists of alternating layers of dielectric materials having high and low refractive indices. The multilayer film -5 of the present invention has a design wave length in the range of l0.84 to 0.92 and preferably within the wave length range of 0.86 to 0.88 micron. This design wave length range is the center of a broad reflectance band chosen to give optimum reflectance of solar infrared radiation and a minimum reflection of solar visible radiation.

Referring to FIG. 3, one type of multilayer film provided for use in the present invention is shown in detail. The film 5 thus illustrated consists of spaced layers of high refractive index materials 6, 7 and 8. Interposed between the high refractive index layers 6, 7 and 8 are low refractive index layers 9 and 10. In actual practice, each of the succeeding layers forming part of the Cil multilayer film 5 are formed by a vapor film deposition. The present invention is not limited to this particular method of thin film application and any suitable conventional method can be employed. The high refractive index layers can be formed of any suitable dielectric material, such as zinc sulfide, zinc oxide, lead molybdate and lead tungstate. Similarly, any Suitable transparent dielectric material having a low refractive index, such as cryolite, magnesium fluoride, lithium fluoride and aluminum fluoride could be used to form the layers 9 and 10.

In connection with the present invention, it has been found that by forming each of the high refractive index layers 6, 7 and 8 and each of the low refractive index layers 9 and 10 with an optical thickness of one-quarter wave length for the maximum wave length to be reflected at the center of the principal reflectance band, optimum results are obtained. For quarter-wave low refractive index layers, the thickness can be determined by the following relationship:

where tL represents the thickness of the low index of refraction layers, ).0 represents the wave length to be reflected at the center of the principal reflectance band, and nL represents the refractive index of the low refractive index layers. Similarly, for quarter-Wave high refractive index layers, the thickness can be determined by the following relationship:

where th represents the thickness of the high refractive index layers, and nh represents the index of refraction of the high refractive index layers.

In the aforementioned copending application Ser. No. 299,851, filed Aug. 5, 1963, it was also described that a terminating layer can be employed to reduce maximum subsidiary reflections which are often obtained in multilayer films. It should be understood that the terminating layer described in the aforementioned copending application can also be employed in the multilayer film of the present invention.

Deposited on the underside of the supporting layer 4 is a single dielectric film 11 having a high index of refraction and also having an over-all thickness determined in the manner set forth in the previously cited copending application. However, it has been found that suitable results have been achieved when the overall thickness of the `dielectric film 11 is Within the range of 1A; to 1/2 wave length for the principal wave length in the wave length range to be reflected. The preferred single dielectric film -11 for the present application is lead oxide. The supporting layer 4 with the films 5 and 11 constitute the second component C2 of the laminate A. The multilayer filrn,5 can be suitably replaced by a dichroic filter 12 substantially as shown in FIG. 4, in order to obtain a high degree of reflectance of infrared radiation. The dichroic filter 12 is similarly deposited upon the plastic layer 4 and includes a metal layer or reflecting surface 13 and one or more dielectric layers 14. The metal reflecting surface 13 is, of course, optically thin and can be vacuum deposited with any suitable metal such as silver, aluminum, zinc, titanium or tin. Increased reflectivity of white light can be obtained by using aluminum, rhodium, and an alloy sold under the trademark Inconel and containing approximately nickel, 13% chromium and 6% iron as the metal reflecting surface. When a metal reflector is employed, the material having the low index 0f refraction is deposited facewise on the metal layer 13. The dielectric layer 14 may consist of a single film of a material having a low refr-active index of the type mentioned or of a multilayer film consisting of alternating layers of high and low refractive index materials. Again, the thickness of the various layers is determined in the manner as previously described.

AWhen using films of a quarter wave length thickness, it is essential that the film of the lower refractive index be deposited on the metallic reflecting surface. The sequence of deposition would then be as follows: metal reflecting surface, low index film, high index film, low index film, high index film, etc. Increased reflectivity may also be obtained if a high index film about one-half wave length in thickness is placed directly on the metal refiecting surface `and then followed with superposed pairs f low-high index films with each film a quarter wave in thickness. The use of a sequence starting with a halfwave high index film on a metallic reflecting surface results in an increased dispersion of the refiectivity which is undesirable when the refiector is to be used with white light. Consequently for metal reflectors employed in the present invention, which are intended for normal use, namely, reflecting solar radiation, the sequence of quarter wave films would be: metal, low index film, high index film, etc.

The third component C3 of the laminate A is then interposed between the thin plastic supporting layer 4 and the panel 1. The component C3 consists of a plastic sheet 15, which is designed to reduce the angular dependency of color. The plastic sheet is preferably formed of the same material from which the layer of plastic material 3 is formed, namely, polyvinyl butyral (plasticized), ethylene-vinyl acetate, hydrolyzed vinyl acetate, cellulose acetate and natural ypolymers with rubber latices having sufficient optical clarity. The most preferred plastic employed is the polyvinyl butyral and is designed to have a thickness of approximately 0.020 of an inch. The plastic sheet 15 `can -be formed with a light-absorbing .medium including pigments such as carbon black, copper phthalocyanine, dibenzanthrone, alizarine cyanine green, indanthrone, chlorinated copper phthalocyanine and others, as well as dyestuffs containing 2 to 4 cyclic nuclei in the color molecule of the type disclosed and claimed in U.S. Pat. No. 2,739,080. The latter include certain azotype dyes illustrated by Kohnstamm Orange, Oil Yellow (Calco), substituted anthraquinones such as Plasto Violet (National Aniline), etc., and mixtures of the same.

The light-absorbing medium is incorporated into the plastic sheet 15 prior to lamination by various practices. When the light-absorbent material is a pigment, it is recommended that it be colloided into a portion of adhesive material, the latter then can act incidentally as at least a temporary support for the light-absorbent materials. The pigment should be uniformly and discretely dispersed throughout the adhesive to produce a lightabsorbing medium exhibiting uniform light absorption. In facilitating this, the pigment should be comminuted to a particle size of about 0.4 micron or less prior to blending with the adhesive. The blended material can then be extruded or cast into a film or layer to serve as a lightabsorbent medium. When the light-absorbent material is a dyestuff, it is preferably deposited from solution onto a layer of adhesive. When the adhesive is a layer of polyvinyl butyral, as in the preferred embodiment, the dyestuff can be caused to diffuse into the adhesive material by aging under slightly heated conditions. Additional adhesive, beyond that which has been used to incorporate the absorbent material to and so form the light-absorbent light medium, can be used to further insure complete lamination between the components of the laminate. Other methods which can be used successfully in forming the light-absorbing medium include brushing, coating, etc. of the light-absorbent material with or without a vehicle including an adhesive directly onto the sheet 15.

The panel 1 which is substantially identical to the panel 2 provides the fourth component C4 of the laminating structure. Naturally, the panels 1, 2 are transparent in the wave length range of light which is to be transmitted. As indicated above, this lower panel 2 is preferably the panel which does not directly receive the incident energy 8 and should have'a low radiation scattering coefficient to provide optical clarity. r

Each of the aforementioned components C1, C2, C3 and C4 is suitably laminated into the composite structure or laminate A as shown in FIG. 1. The four components are facewise disposed upon each other in marginal registration and in the selected order shown in FIG. 2 in the` laminating operation. The stacked components are then placed in a laminating chamber which is evacuated to a pressure of approximately 1 millimeter of mercury. Thereafter, the composite structure is heated to atemperature within the range of v to 230- F. The-preferred temperature employed when the panels 1,` 2 are glass and the plastic material employed is polyvinyl butyral is 200 F. After the composite structure has reached the preferred laminating temperature, pressure is applied to all exposed surfaces of the composite structure.v The preferred pressure is approximately- 200 pounds per square inch. The composite structure is then maintained at this preferred laminating temperature and laminating pressure for approximately 5 minutes. Thereafter, the temperature is reduced and the pressure is released and the various components C1, C2, C3 and C4 are molded in the laminate A.

By means of the above outlined method, a substantially clear and optically efficient laminate is achieved which is capable of reflecting a high percentage of infrared radiation and of selectivity transmitting radiation in the visible wave length range. It is to be noted that pressure is vnot only maintained on the upper and lower surfaces of the panels 1, 2 providing facewise forcing engagement of the various components but is also maintained on the side margins of each of the components.

In the laminated structures containing dichroic filters heretofore provided, the filter which usually consisted of a multilayer dielectric film was destroyed or suffered some distortion in the laminating process. Generally, the multilayer film was disposed between overlying and underlying layers of plastic material. The plastic material did not necessarily serve a structural function but may have served as an adhesive. Moreover, the plastic layer may not have been of a thickness to be considered an optically massive structure but it was of sufficient thickness to destroy the dichroic filter in the laminating process. Under the extreme pressure maintained in the laminating operation, the plastic material disposed in facewise engagement of the film of the dichroic filter would yield and the filter would crack into small particles. In fact, it was normally found that the filter would crack into particles having an overall length of 0:001 to 0.10. When considering the overall thickness of the plastic layer in faeewise engagement withthe filter -within this dimension, rit can be realized that these various particles became randomly disoriented.-While this does not always interfere with heat transmittance and refiectance, it virtually destroyed optical clarity, and moreover,` interfered withcolor transmittance at various angles of incidence of view.

In the present method, the multilayer film `5 is supported on a plastic layer 4 and moreover is in substantial facewise engagement with a relatively hard panel 2. Actua'lly, the multilayer film S is inengagementwith the, plastic film 3, but the latteris sufiiciently thin so that for all practical purposes, the multilayer film 5 is retained in and even larger.` In many cases, ,very large particles or" as much as 0.25 of an inch were observed. When it-.is

realized that they can only vbecome* disoriented in the',

planar direction through the plastic layer 3 having a thickness of 0.5Y to 1.0 micron, it can be seen that the:

disorientation is very slight. Accordingly, excellent results have been achieved by the aforementioned laminating process.

It is possible to provide a modified form of laminating process in accordance with the present invention, which is more fully illustrated in FIG. 5. In the laminate B illustrated in FIG. 5, relatively fiat panels 16, 17, which are substantially identical to the previously described panels 1, 2 respectively, are employed. A thin plastic layer 18 Substantially identical to the previously described layer 3 is also deposited on the underside of the upper panel 17. A thin plastic supporting sheet or layer 19 similar to the supporting sheet 4 is provided with a dichroic filter 20 on its upper surface which is also substantially identical to the multilayer film 5. IIn this case, it should also be understood that the filter 20 may consist of a multilayer film having a plurality of dielectric layers substantially as shown in FIG. 3. It may also consist of the metallic reflecting layer with one or more dielectric layers substantially as shown in FIG. 4. The underside of the fiat sheet 19 is provided with a single dielectric layer 21 substantially identical to the dielectric layer 4. This structure is then suitably laminated to a plastic layer 22 which is substantially identical to the plastic sheet 15.

In this maner, a three component structure is provided in the laminating process. The panel 17 with the lower coating of plastic 18 constitutes the first component C5. The second component C6 consists of the plastic layer 22 with the supporting plastic layer 19 having a filter 20 and a layer 21 thereon in a single composite structure. The third component C7 includes the lower panel 16. In this embodiment of the invention, the three components are stacked in marginal registration in the manner as shown in FIG. 5. The laminating procedure conducted is thereafter substantially identical to the laminating procedure described in the previous embodiment. It has again been found that the structure thus produced is a laminate of high optical clarity and exhibits good reflectance of infrared radiation and good selective transmittance of visible radiation.

In connection with the present invention, it should be understood that the layers of plastic and 22 can be suitably incorporated with a conventional dye. In the prior art, the dye often interfered with the optical clarity and different colors were observed when the structure was viewed at various angles of incidence with respect to the normally flat surfaces thereof. The single dielectric film 11 and the dielectric layer 21 serve to decrease the angular dependence of color and consequently, it is now possible to add a suitable dye without obtaining undesired color rendition.

It is possible to provide another modified form of laminating process in accordance with the present invention which is more fully illustrated in FIG. 6. According to this process, a laminate D is formed by relatively flat upper and lower panels 23, 24, which are substantially identical to the previously described panels 1, 2 respectively, and are transparent within the wave length range of radiation to be transmitted. A thin plastic supporting sheet or layer 25 substantially similar to the supporting sheet 4 is lprovided with a dichroic filter 26 on its upper surface which is substantially identical to the multilayer film 5. In this modification, it should also be understood that the dichroic filter 26 may consists of a multilayer film having a plurality of dielectric layers substantially as shown in FIG. 3. It may also consist of the metallic reliecting layer with one or more dielectric layers substantially as shown in FIG. 4. The underside of the relatively fiat suporting sheet 25 is provided with a monolayer dichroic filter or single dielectric layer 27, which is substantially identical to the dielectric layer 4.

Deposited on the upper surface of the dichroic filter 26 is a relatively thin plastic material layer 28 of not less than 0.05 micron thick and not greater than 10.0 microns thick and which is substantially identical to the thin plastic layer 3. This thin plastic layer was previously deposited on the underside of the panel 2 in the previous embodiment of this invention. It can thus bevseen that in this embodiment of the invention, the plastic layer 28 is no longer deposited on the underside of the panel 23 but rather on the upper surface of the dichroic filter 26. The thin plastic layer 28 may also be thermoplastic or thermosetting in nature and may be any of the plastic materials from which the layer of plastic material 3 is formed. A plastic sheet 29, which is substantially similar to the plastic sheet 15, is provided for deposition between the supporting sheet 25 and the transparent panel 24. The plastic sheet 15 is also designed to reduce the angular dependency of color in the laminated structure and is formed of any of the materials from which the plastic sheet 15 is formed. Again, suitable light-absorbing pigments may be incorporated in the sheet of plastic 29.

In this manner, a four component structure is provided in the laminating process. The upper panel 23 constitutes the first component C8. The second component C9 consists of the thin plastic supporting layer 25 with the dichroic filters 26, 27 on opposite sides thereof and the thin plastic layer 28 on the upper surface of the dichroic filter 26. The third component C10 consists of the relatively thick plastic sheet 29 and the fourth component C11 consists of the bottom panel 24. In this embodiment of the invention, the four components are stacked in marginal registration in the manner as shown in FIG. 6 and the laminating procedure conducted thereafter is substantially identical to the laminating procedure described in the previous embodiments of this invention.

It has again been found that this structure produces a laminate of high optical clarity and which exhibits good reflectance of infrared radiation and good selective transmittance of visible radiation. This type of laminating structure has a distinct advantage over the previously described embodiment in that the component C9 is sufficiently fiexible so that it can be rolled for storage and shipment. As previously indicated, the thin plastic supporting layer 25 has a thickness preferably within the range of 0.00025" to 0.0050". The lower size limitation is determined so that the layer 25 has sufficient supporting strength. The plastic layer, when formed of polyvinyl butyrol is so thin that it can be rolled or folded without destroying the plastic sheet. Moreover, the dichroic filters deposited thereon are suiciently thin so that thep will not be destroyed or in any way deleteriously affected if the component C9 is rolled. Obviously, great pressure cannot be applied to this particular component due to the fact that extreme pressures may crack one or both of the dichroic filters on the supporting sheet 25.

It is possible to provide an additional modified form of laminating process in accordance with the present invention, which is more fully illustrated in FIG. 7. The laminate E produced by this process comprises relatively fiat spaced opposed panels 30, 30', which are substantially identical to the previously described panels 1, 2 and are transparent within the wave length range of radiation to be transmitted. A thin plastic'supporting sheet 31 similar to the supporting sheet 4 is provided with a dichroic filter 32 on its upper face, which is also substantially identical to the previously described multilayer film 5. In this embodiment, it should be understood that the filter 32 may consist of a multilayer film having a plurality of dielectric layers, substantially as shown in FIG. 3. It may also consist of the metallic reflecting layer with one or more dielectric layers substantially as shown in FIG. 4. The underside of the relatively flat sheet 31 is provided with a single dielectric layer 33 serving as a filter which is substantially identical to the previously described dielectric layer 4.

Deposited on the upper surface of the dichroic filter 32 is a relatively thin plastic polymerizable sheet or layer 34 which is substantially identical to the previously described layer 31 also formerly deposited on the underside `of the panel 17. The plastic layer 34 may be thermoplastic or thermosetting in nature and may be formed of any of the materials from which the plastic material 3 is formed. Actually, it should not Jbe less than 0.05 micron and not greater than 10.0 microns thick. This structure is suitably laminated to a plastic layer 35, which is substantially identical to the plastic sheet 15.

,In this manner, a three component structure is provided in the-laminating process. The upper panel 30 constitutes the first component C12. The second component C13 comprisesl the thin plastic supporting sheet 31 with dichroic filters 32, 33, the polymerizable plastic layer 34 and the thick plastic layer 35. The third component C14 includes the lower panel 30. In this embodiment of the invention, the three components are stacked in marginal registration in the manner as shown in FIG. 7. The laminating procedure is thereafter substantially identical to the laminating procedures described in the previous embodiments of this invention. It `has again been found that the structure produced in this embodiment is a laminate of high optical and good selective transmittance of visible radiation.

THEORY In order to understand the calculations of effective transmittance and absorbance of radiation in the laminated structures previously described, the following optical theory has been developed and is deemed to be of pertinence. The following theory will provide dimensions for the calculations for the properties of the laminates when given the reflectance, transmittance and absorbance as functions of wave lengths (or mean values of these properties over a wave length interval) of the panels and coatings. It can be assumed that the transmittance tg of the glass is determined by direct measurements and that refiectance rg and that absorbance ag are directly calculatable from the transmittance and refractive index. In general, the properties of the coated structures are different for incidence from each side and the calculations take this difference into consideration. Accordingly, energy distribution patterns have been established for each of the panels which comprises the laminate substantially as shown in FIGS. 8 and 9. In FIG. 8, a ray diagram is illustrated for coated glass where the radiation is incident on the glass side and'not the surface having the coating. In lFIG. 9, a ray diagram is presented Where the radiation is incident on the coated side of the glass surface. FIG. is a composite ray diagram for the laminated panels shown in FIGS. 8 and 9. For the following mathematical description, the following properties are defined.

Glass-For a sheet of glass, we define the properties:

p=refiection coefficient at the air/glass interface dritti) a=the linear absorption coefficient and x=distance traversed by the radiation and will usually be taken as the thickness (or slant thickness) of the glass.

Transmittance.-Glass tz=transmittance of glass plate transmitted intensity l p) Ze-X incident intensity l-pe2Dtx (5a) :e =(1-p)2ex(for 10W p) (5b) l1 -1 l p (for low a) (5C) z =(1-p)2(for 10W aiA and p) (5d) t a O.D.-opt1cal density-log tg-log I (6) 1 p2e-2ax C dilog 'r1-n2 L2-3 (o For small p, Eq. 7 becomes all? O.D.--log (l-p)2 (8) For glass, where p is small, usually about 0.04, the internal transmittance is obtained from Eqs. 4 and 5b as t ^r=(l p)- (for small p) (9) Reflectance.-Glass I (reflected) rz reectance of glass plate- I- -0(nci dent) p)2e2ax "pipf l-pe-mi 10) E. 1+pfor1owa (1l) z =p[1+(1p)2f2]=p [1+(Tp-)Z (for 10W a) Absorbance.-Glass I (absorbed) cigabsorbance of glass plate I- 0 (incident) :Sir-p) (1-6ax) l pe""x (13) o-p) 1-f) Having thus defined the properties of the glass or transparent laminates, it is now necessary to define the properties of the multilayer films and monolayer films ernployed in the present invention. For the purpose of this theory, the films, both multilayer and monolayer, will be referred to as coatings, andthe properties of the coatings will be designated by a subscript c. Before examining the energy distribution for the composite laminated structure, it is necessary to examine the energy distribution of each panel with its associated interference filter.

As previously indicated, two interference filters are provided in each of the embodiments of the present invention. One of the interference filters is a multilayer film which may consist of a metallic layer and one or more dielectric layers or just a series of dielectric layers. The other interference lter is the monolayer lter preferably formed of lead oxide. The thin plastic material 3 on the underside of the panel 2 does not in any way interfere or affect the energy distribution through the panel. Accordingly, FIG. 8 represents the panel 2 with the multilayer film S on the inner surface thereof. The transparent panel in FIG. 9 represents the transparent panel 1 with the thick laminatable plastic Iand the interference filter 11 on one fiat surface. The plastic sheets employed in the present invention have refractive indices which are substantially similar to the outer panels so that the refiection at the panel-plastic interface is negligible, though reectance occurs at the interface of the combined panel and plastic sheets with the interference filters. Accordingly, FIGS. 8, 9 and 10 are representative of the schematic energy distribution through the laminates of the present invention.

Results are given in terms of transmittances (percentage) and means transmittances for films on glass substrates. The effect of the glass/coating interface is included as a property of the coating. This has been taken into account in using measured transmittances of glass. It has been shown that transmittance and reflectance each have the same values for incidence from either the glass or the air side of the coating. For the MLF coatings the following properties are dened:

tc=transmittance of coating (from computer program) rc=retlectance of coating ac=absorbance of coating.

Having thus described the denitions of the properties of the coatings, it is possible to establish equations for the reectance, transmittance and absorbance of energy on a single panel Where radiation is incident upon the glass side. Schematic energy distribution for this panel is illustrated in FIG. 8. In this diagram the fractional distribution of energy of an incident ray is shown. Summation of these rays gives the distribution of intensity between reflection, transmission and absorption.

Reection.-From FIG. 8 the rellectance r, is given by Absorption-From FIG. 8 the absorbance for incidence on the glass sides is seen to be Transmission.-From FIG. 8 the transmittance for incidence on the glass side is It is possible to establish a check for the equations determining the rellectance, absorbance and transmittance of energy -where radiation is incident on the glass side. The sum of reected, absorbed, and transmitted intensities should equal the incident intensity, i.e.

14 tion of this panel is illustrated in FIG.'9. In this diagram, the fractional distribution of energy of an incident ray is shown. Summation of these rays gives the distribution of intensity between reflection, transmission and absorption.

Reflection- From FIG. 9 the rellectance, r, for incidence on the coated side is given by (C) Absorption for incidence on coated side- From FIG. 9 the absorbance is It can be seen that this was the same result as Was obtained for transmission for incidence on the glass side, Equation 20, when We substitute `(l-r-ac) for tc. This result is consistent with measurements on anisotropic retiectors prepared by vacuum evaporation of metal and dielectric thin lms.

It is also possible to establish a check of theequations for the reflectance, absorbance and transmittance of energy where radiation was incident on the coated side of the panel. The sum of reected, absorbed, and transmitted intensities should equal the incident intensity, taken as unity, i.e.

r+a+t=1 To test this add Equations 22, 24 and 25, obtaining,

Now rc-|-ac-|-tc=l or t-|ac-1=rc, hence the expression in brackets equals unity so that equation reduces to r-|-a|-t=rc|ac+tc, bot-l1 sides of which equal unity, showing that the derived equations fit the above stated condition required for a check.

'It is now possible to calculate the reflectance Rc, the absorbance Ac and the transmittance Cc -for the composite laminate structures illustrated. A ray diagram for this calculation is provided in lFIG. l0. For the ray diagram of FIG. 10, the ray diagrams of single panel structures in FIGS. 8 and 9 were combined. For t-he outer sheet, a subscript 1 will be used for the reflectance, absorbance and transmittance. For the inside sheet, the subscript 2 will be used in these relationships. The following equations relate the properties of the laminate to properties of individual sheets. The measured or calculated properties of individual coated sheets can be used to calculate the properties of the composite structure or laminate. The following relationship provides a measurement of the outside reectance.

The above relationship shows a strong dependence on the transmittance t, and indicates that for heat reflection, the outer panel must have high transmittance.

The following relationship provides the absorbance of The following relationship provides the transmittance of the inside sheet.

tltz T C 1 -zrfir 'Ihe following relationship provides the absorbance of the inside sheet.

As an outer sheet the radiation will be incident on the glass side (designated back side, subscript b to be added to r, a, and t), while as an inner sheet the radiation will be incident on the coated side (designated front, subscript f). The quantities, r, a, and t calculated by Equations 16, 18, and thus become rlb, alb, and tlb when for an outside sheet for incidence on the glass (back) side, and Equations 22, 24, and give ru, au, tu. For the inside sheet the subscript 1 would become 2.

Since we are interested in the effect of solar energy, Rs, As and Ts used are the mean values for several spectral ranges of the solar spectrum weighted against the intensity of solar radiation. For example, the visible reflectance of one particular sheet is where `=wave length rx=reectivity at )t G=sola.r radiation intensity at )t rv1s=mean reflectivity for visible radiation having the distribution of the suns visible radiation.

'Ihe invention is further illustrated by but not limited to the following examples:

Example 1 A number of laminates employing different types of dichroic filters and different types of panels were analyzed for visible transmittance, heat reectance, heat admittance, heat rejection and heat absorbance. The following table sets forth the data for the various laminates analyzed.

SOLAR ENERGY PERFORMANCE l 0F MLF COMPOSITE LAMINATES (PERCENT) Sample A B C Visible reflectance:

Insi e Visible transmittance Heat reflected Heat admitted Heat rejected Heat absorbed by outer sheet 2 l Results are for angle of incidence of solar radiation at sea level after traversing two air masses. Data for the visible range are percent of visible energy. Data for "heat reflected, etc., are percent of total solar energy.

2 Values in parentheses are total energy absorbed by the laminates.

Sample A employed a 1A thick outer panel ormed of Pittsburgh Plate Glass Company Pennveron Graylite GL-31 glass. The inner panel was of equal thickness and formed of Pittsburgh Plate Glass Company Pennveron Graylite GL-6l. 'Ihe plastic layer employed was a 0.020" thick layer of plasticized polyvinyl butyral sold under Monsanto Companys trademark Sailex 'Ihe solar energy transmittance of the two panels which were employed in this example is set forth below.

TABLE I.-SOLAR ENERGY TRANSMITTANCE OF PENN- VERNON GRAYLITE SHEET GLASS AT 30 ANGLE OF INCIDENCE Range of total lite 30 lite 30 (microns) energy incidence incidence incidence 0.3-0.4 2. 7 65. 1 71. 7 72. 6 0. 4-0. 7 44. 4 18. 1 35. 4 62. 0 0 7-1. 12 36. 4 59. 5 73.6 78. 2 1 12-1. 38 8. 6 49. 3 59. 0 74. 5 1 38-1. 85 6. 6 54. 9 70. 1 79. 6 l -2. 14 1. 2 50.8 68. 4 78. 3 0. 3-2. 14 100. 0 40. 0 55. 0 70. 6 0. 7-2. 14 52. 8 57. 0 70. 6 77. 8 Thickness, lx1 7/32 D.S. 3/16 The angle of incidence employed for the measurement of 30. The iilter employed Iwas a three layer multilayer film consisting of alternating layers of lead oxide and` cryoliite. Lead oxide formed the outer llayers which is the high index of refraction material and the inner layers are cryolite which is the low index of refraction material. The single layer dielectric material was lead oxide. Each of the aforementioned layers had 1A wave length thickness.

The sample B was substantially similar to the sample A except that the sample employed a 7 layer multilayer film consisting of alternating layers of lead oxide and cryolite each having a thickness of 1A wave length.

Sample C was substantially similar to sample B except that the sheets of glass were separated by a relatively thin air space.

Sample D differed from sample A in that the dichroic filter employed was a seven layer lm, four layers of which had an index of refraction of 2.4 and 3 alternating layers which had an index of refracltion of 1.37. The wave length of the film was also designed to be 0.90.

Sample E was substantially similar to sample A except that the Safiex layer was eliminated and an air gap of the same thickness was employed.

The results obtained are for an angle of incidence of 30 of solar radiation at sea level. The data for the visible range is given inthe precent of visible energy. The data for the heat reflected, the heat admitted, the heat rejected, and the heat absorbed is given in percent of the total solar energy.

Example 2 The heat insulating and glare reducing properties of a pellucid laminate constructed in accordance with the present invention were determined in this example. The laminate formed was of the type illustrated in FIGS. 1 and 2 and consisted of outer glass panels each of |which was suiciently thick to constitute massive layers. The thin layer of laminatable plastic 3 on the underside of the panel 2 was formed of plasticized polyvinyl butyral having a thickness of 1 micron. The supporting lm for the interference filters was formed of a jelled cellophane material and had a thickness of 0.001. The upper surface of the supporting layer `4 was provided with a multilayer film consisting of four alternating layers of lead oxide and three alternating layers of cryolite. The multilayer film was designed with a wave length of 0.88 micron. The single layer fihn was formed of lead oxide with an overall thickness which is equal to one fourth the design wave length 'range to be reflected. The single layer lm was designed with a wave length of 0.88 micron. The thick plastic layer 15 was formed of four diierent materials and the properties of the pellucid laminate was determined in each of these four cases.

TABLE IL PERCENT The heat rejected considering a conduction factor of onehalf each way was 53 .6%. The heat rejected considering a conduction factor of two-thirds to the outside and onethird inside was 57.3%.

In the second case, the same laminate was employed except that the layer was formed of a plasticized polyvinyl butyral having a suitable neutral absorbing additive content to give 55% transmittance. The absorbing additive may be any of the neutral additives listed above which are suitable for incorporation into the layer 15. This plastic layer is sold under the trademark Shadowlite 55. Reflectance and transmittance data was determined for each of the 'three wave length ranges and the total thereof at an angle of incidence of solar radiation at 30.

TABLE IIL-PERCENT R300 Tao Ultraviolet 18. 3 8 Visible 22. 3 26. 0 Infrared 60. 6 15. 0 al 42. 5 19. 4

TABLE IV.PERCENT Rana T3o Ultaviolet 18. 3 4 Visible 22.3 13. 2 Infrared 60. 6 7. 6 Total 42. 5 9. 9

Considering an absorbance factor of one-half, the total heat rejection was 66.3%. Considering an absorbance factor of two-thirds, the total heat rejection was 74.1%.

The same plastic laminate was again employed except that the layer 15 was formed of dry air. The reflectance and transmittance of each of the above wave length ranges and the total was established when solar radiation was directed on the laminate at an angle of incidence of 30.

TABLE V.PERCENT Considering a heat conduction factor of one-half, the total heat rejection was 57.4%. Considering a heat conduction v in the form, construction, arrangement and combination of parts presently described and pointed out may be. made and substituted for those herein shown without departing from the nature and principle of my invention.

What is claimed is:

1. The method of making a pellucid laminate, including a pair of outer panels and an inner panel with interference lilter disposed between said inner and outer panels for selective reflectance and transmittance of selective radiation over an extended wavelength range, said method comprising:

(a) depositing a thin layer of a plastic on the inner face of one of said outer panels to form a iirst component,

(b) depositing a first interference filter on one fiat surface of a plastic support,

(c) depositing a second interference filter on the opposite flat surface of said plastic support forming a second component,

(d) incorporating radiation affecting additives in said inner panel forming a third component,

(e) the other of said outer panels serving as a fourth component,

(f) stacking each of the aforementioned components in marginal registration, and

(g) laminating each of the aforementioned components under conditions of heat and pressure to form a pellucid laminate.

2. The method of claim 1 further characterized in that said thin layer of plastic is polymerizable.

3. The method of making a pellucid laminate including a pair of outer panels and an inner panel with interference filters disposed lbetween said inner and outer panels for selective reectance and transmittance of selective radiation over an extended wavelength range, said method comprising:

(a) depositing a thin layer of plastic on the inner face of one of said outer panels to form a first component,

(b) incorporating radiation absorbing additives in said inner panel,

(c) depositing a lirst interference iilter on one liat surface of said inner panel,

(d) forming a support layer of plastic on said rst interference filter,

(e) depositing a second interference ilter on said support layer of plastic to form a second component,

(f) the other of said outer panels serving as a third component,

(g) stacking each of the aforementioned components in marginal registration, and

(h) laminating each of the aforementioned components under conditions of heat and pressure to form a pellucid laminate.

4. The method of claim 3 further characterized in that said thin layer of plastic is polymerizable.

5. The method of making a pellucid laminate, including a pair of outer panels and an inner panel with interference filters disposed between said inner and outer panels for selective reiiectance and transmittance of selective radiation over an extended Wavelength range, said method comprising:

y(a) the first of said outer panels serving as a rst component,

(b) depositing a first interference lilter on one at surface of a plastic support,

(c) applying a thin plastic layer to the exposed surface of said filter,

(d) depositing a second interference filter on the other flat surface of said plastic support to form a second component,

(e) incorporating light affecting additives in said inner panel forming a third component,

(f) the other of said outer panels serving as a fourth component,

(g) stacking each of the aforementioned components in marginal registration, and

(h) laminating each of the aforementioned components under conditions of heat and pressure to form a pellucid laminate.

6. The method of making a pellucid laminate including a pair of outer panels and an inner panel with interference filters disposed between said inner and outer panels for selective reectance and transmittance of selective radiation over an extended Wavelength range, said method comprising:

(a) one of said outer panels serving as a first component,

(b) incorporating radiation absorbing additives in said inner panel,

(c) depositing a first interference filter on one flat surface of said inner panel,

(d) forming a support layer of plastic on said rst interference filter,

(e) depositing a second interference filter on said support layer of plastic,

(f) forming a thin layer of plastic on the exposed fiat surface of said last named yfilter to form a second component,

(g) said other outer panel serving as a third component,

(h) stacking each of the aforementioned components in marginal registration, and

(i) laminating each of the aforementioned components under conditions of heat and pressure to form a pellucid laminate.

7. The method of making a pellucid laminate, including a pair of outer panels and an inner panel with interference filter disposed between said inner and outer panels for selective refiectance and transmittance of selective radiation over an extended Wavelength range, said method comprising:

(a) depositing a thin layer of polymerizable plastic on the inner face of one of said outer panels to form a first component underside,

(b) depositing a first interference filter on one flat surface of a plastic support,

(c) depositing a second interference filter on the opposite at surface of said plastic support forming a second component,

(d) incorporating radiation affecting additives in said inner panel forming a third component,

(e) the other of said outer panels serving as a fourth component,

(f) stacking each of the aforementioned components in marginal registration, and

(g) laminating each of the aforementioned components under conditions of heat and pressure to form a pellucid laminate.

8. The method of making a pellucid laminate, including a pair of outer panels and an inner panel with interference filter disposed between said inner and outer panels for selective reflectance and transmittance of selective radiation over an extended wavelength range, said method comprising:

y(a) depositing a thin layer of polymerizable plastic on the inner face of one of said outer panels to form a first component underside,

(b) depositing a rst interference filter on one fiat surface of a plastic support,

(c) depositing a second interference filter on the opposite flat surface of said plastic support forming a second component,

(d) incorporating radiation affecting additives in said inner panel forming a third component,

(e) the other of said outer panels serving as a fourth component,

(f) stacking each of the aforementioned components in marginal registration, and

(g) laminating each of the aforementioned components under conditions of heat and pressure to form a pellucid laminate.

References Cited UNITED STATES PATENTS 2,624,239 l/1953 Blout et al. 156-99 X 3,069,301 12/1962 Buckley et a1 156-99 X CA'RL D. QUA-RFORTH, Primary Examiner H. E. BEHREND, Assistant Examiner U.S. C1. XJR. 156-106 

